Method for minimizing curling in screen printing

ABSTRACT

A method of silk screen printing on a piece of paper, such as poster paper, in which a first silk screen printing is effected onto the sheet utilizing a printing ink that produces minimal curl in the edge of the sheet, and at least one subsequent silk screen printing is effected onto the sheet utilizing a water-based printing ink. The resulting curl is less than that which would be obtained if the first screen printing were made with the water-based ink.

This invention relates to printing and in particular to screen printing(commonly known as silk screen printing). As is well known, the silkscreen printing process involves the use of a screen of silk, polyester,nylon, metal gauze or any other suitable mesh-like or perforatedmaterial. For convenience (and for consistency with the terminologyhistorically employed in this art) the term "silk screen printing" willbe used herein and it will be appreciated that no restriction to "silk"material is thereby intended.

Although silk screen printing is a very old technique, it still hasnumerous problems and/or limitations associated with it. For example,where several large-size multi-color sheets are to be silk screenprinted for, say, a poster to be pasted up on a hoarding, largequantities of printing inks are needed which are expensive.

The printing inks required for screen printing are quite different fromthose to be used for other forms of printing. The screen printing inksbeing generally used at present are organic solvent-based and usuallycontain ethyl or nitro cellulose resins. They are dried in warm airtunnels by driving off the organic solvents, and are thus potentiallyhazardous to the printing operatives. Another problem which arises withsuch organic solvent-based screen printing inks, relates to solvent lossfrom the ink on the printing screen whereby the ink increases inviscosity and after a certain period of time will not properly passthrough the open areas of the printing mesh. This "drying in" results inloss of printed image and is described as screen stability, i.e. inkswith poor screen stability "dry in" rapidly.

Recent developments over the last ten years have seen the introductionof ultraviolet-curing screen process inks.

Here the formulations use raw materials which do not increase in theirviscosity on the printing screen but instead dry by exposure to intenseultraviolet (UV) light. This means that this type of ink has almostunlimited screen stability compared to non-UV curing, organicsolvent-based, screen printing inks. However, such UV-curing inks areexpensive, and leave a very thick print coat on the paper surface --particularly where multi-color, e.g. four-color, silk screen printing iseffected.

Such thick or heavy print images on the surface of a sheet of posterpaper often necessitate that for mounting the poster to its hoarding, aspecial adhesive -- which is other than an inexpensive starch-basedadhesive -- must be used if efficient bonding is to be achieved. Asimilar problem often arises with the older type of organicsolvent-based silk screen printing inks. This adhesion problem is commonwhere the individual sheets overlap, e.g. at overlapping marginal edgesof adjacent poster sheets. The back of the top sheet does not havesufficient adhesion to the ink dries out, the top sheet of the overlapoften curls up and away from the sheet underneath. The problem isparticularly severe when the paper is completely covered with severallayers of ink. Posters printed with offset litho inks have less tendencyto curl when they dry out compared to those produced with screenprinting inks. As the screen printing process achieves its high qualityprint appearance by a much higher ink deposit, the curl problem ispronounced with screen printing inks. Therefore the adhesives used withscreen printed posters need to have better adhesion properties toprevent overlap curl.

Mixtures of one or more starch adhesives and one or more polyvinylalchol (P.V.A.) adhesives were investigated by the applicants, and thesewere found to give a much improved adhesion at the overlapping edges ofsuperimposed sheets as compared to a 100% starch-based adhesive product.However, mixtures of starch and P.V.A. adhesives have the disadvantageof being more expensive and the resultant improved adhesion makes theremoval of the total poster from the hoarding more difficult. Thus theyare not likely to find favour with bill-posters, i.e. those responsiblefor putting up the posters on the hoardings.

It is therefore considered desirable to reduce, if not wholly obviate,some or all of the above-mentioned and/or other disadvantages associatedwith or relating to prior art screen printing methods and inks.

According to one aspect of this invention there is provided a method ofsilk screen printing on a sheet of paper or board, characterised in thata first silk screen printing is effected on the sheet utilizing aprinting ink that produces minimal curl, and in that at least onesubsequent silk screen printing is effected on the sheet utilizing awaterbased printing ink.

By effecting said first printing with an ink that produces minimal curl,the printed sheet can be readily fed again through the screen printingmachine to be overprinted with the subsequent printing(s).

Said first silk screen printing may be effected utilizing anorganic-solvent-based printing ink, or a non-aqueous printing ink thatis curable by irradiation, or an aqueous ink of high solid and low watercontent, e.g. water content less than 20%.

It is considered that the printing ink used for the first printing ineffect seals the surface of the paper sheet thereby reducing the risk ofdamage to the sheet from the water content of the water-based printingink.

Preferably, the first silk screen printing is in a first color and theor each said subsequent printing is in a different color.

Preferably, said water-based printing ink used for the or eachsubsequent printing is at least partially curable by irradiation. Asused herein in relation to curing, the term "irradiation" refers toelectromagnetic radiations having wavelengths shorter than those of thevisible spectrum. The term thus includes ultraviolet (UV) and electronbeam radiations.

Preferably, the water-based printing ink used for the or each subsequentprinting comprises one or more photoinitiators and is at least partiallycurable by irradiation comprising electromagnetic radiations in theultraviolet light waveband.

Alternatively, the water-based ink used for the or each subsequentprinting may be at least partially curable by irradiation with anelectron beam. Where the ink is curable by irradiation with an electronbeam, then photoiniator(s) may be omitted from the printing inkcomposition.

Preferably, and in either case, the water-based printing ink used forthe or each subsequent printing is subjected to heat or to thermalradiation, e.g. is subjected to electromagnetic radiations in theinfrared light waveband, prior to curing. Alternatively, the print issubjected to cold air from a jet air dryer or is subjected to microwaveor radio frequency drying.

Preferably said water-based ink used for the or each subsequent printingcomprises an unsaturated acrylate resin, e.g. a polyester acrylateresin.

Advantageously, the water-based screen printing ink used for the or eachsubsequent printing comprises an emulsion of a resin in water.

Preferably the emulsion has said resin wholly, or at leastsubstantially, as the dispersed phase and wholly, or at leastsubstantially, insoluble in water, water being the continuous phase ofthe emulsion.

Advantageously said resin comprises 30% to 60% (preferably 50%) of theemulsion.

Preferably, said method is employed to screen print a plurality ofcolors upon a sheet and, after printing, the printed sheet is subjectedto corona discharge to render the sheet readily mountable, e.g. upon ahoarding, by use of a starch-based adhesive.

It is considered that the corona discharge provides minisculeperforations through the printing ink which enable the adhesive toextend through the sheet to provide a "keying" effect facilitating theefficient bonding together of overlapping marginal edges of adjacentsheets.

The following relates to the production of individual silk screenprinted sheets and their treatment for application onto hoarding sitesin accord with embodiments of the present invention. As well as singlesheet posters, the embodiments are concerned with the usual combinationsof multiple sheet posters (e.g. "16 sheet", "48 sheet" or "96 sheet"posters) for pasting up onto large hoardings. The screen printing methodused in these embodiments may be for the production of four colorhalftone prints as well as continuous line and tone color prints.

The following embodiments of this invention concern the screen ink usedto print the sheets.

In one preferred form of a "four-color printing" screen processembodying the present invention, the first color printed is with anon-aqueous UV-curing printing ink of cyan shade, e.g. a screen inkhaving a composition in accord with Example 6 below.

In another preferred form of the "four-color printing" screen process,the first color printed is with an organic solvent-based printing ink ofcyan shade, e.g a screen ink, having a composition in accord withExample 7 below.

In yet another preferred form of the "four-color" screen printingprocess, the first color printed is with a slightly aqueous (i.e. lessthan 20%), predominantly solids (i.e. greater than 80%), screen printingink of appropriate, e.g. cyan, shade The screen ink employed for thefirst printing in this case preferably has a composition in accord withExample 8 below.

Although in each of these three cases the screen ink employed for thefirst color is of cyan shade, it will be appreciated that the color canbe any other primary trichromatic color, and usually will be thepredominant or principal color produced by the photographic colorseparation of the original.

In the following preferred embodiments of the invention, each of thesubsequent colors printed in superimposition on the first color, isscreen printed in a water-based, UV-curing ink. In thee preferredembodiments the water-based, UV-curing screen ink comprises an emulsionof a resin in water, said resin being wholly (or at least substantially)in dispersed phase and wholly (or at least substantially) insoluble inthe water, the water being the continuous phase of the emulsion. Thusthe screen printing ink employed for the or each subsequent printingcontains water, is water miscible and is water thinnable to aconsiderable extent, but the water is to be regarded as a carrier ordiluent (rendering the ink aqueously reducible in viscosity) rather thanas a solvent Preferably the ink employed for the or each superimposedprinting contains at least 40% water.

In a first embodiment of this invention the water-based printing inkemployed for the or each subsequent printing has a compositioncomprising an ultraviolet curing resin emulsified with water, aphotinitiator and an aqueous pigment dispersion One specific formulationof this, in which the emulsion has the resin amounting to 50% of theemulsion, is given in Example 1 .

    ______________________________________                                        Example 1              Parts by weight                                        ______________________________________                                        Emulsion Laromer* PE 55W.sup.(1)                                                                     95.3                                                   Darocur* 1173.sup.(2) Photoinitiator                                                                 2.0                                                    Aquadisperse Phthalo Blue GB EP.sup.(3)                                                              2.7                                                    ______________________________________                                    

A composition as formulated in Example 1 was printed through a screenmade from 165 threads per cm polyester mesh half-calendered. Thecalendered side was positioned face down towards the substrate, ie M.G(machine glazed) poster paper. The stencil was made from direct emulsionusing a half-tone positive The print was produced on an S.P.S. cylinderaction screen printing press. The ink was dried through a two lampS.P.S. UV dryer (rated at 300 watt per inch). The resultant dried printwas a good half tone image of high definition.

However, this initial formulation, when tested, gave poor screenstability. This was improved, in a second embodiment, by the addition ofn-vinyl pyrrolidone -- a solvent miscible with water which also takespart in the curing reaction. A specific formulation of this secondembodiment, which likewise has the resin amounting to 50% of theemulsion), is given in Example 2.

    ______________________________________                                        Example 2              Parts by weight                                        ______________________________________                                        Laromer* PE 55W.sup.(1)                                                                              85.3                                                   Darocur* 1173.sup.(2)  2.0                                                    Aquadisperse Phthalo Blue GB EP.sup.(3)                                                              2.7                                                    n-vinyl pyrrolidone.sup.(4)                                                                          10.0                                                   ______________________________________                                    

A composition as formulated in Example 2 was printed and dried in thesame manner as for Example 1. The resultant dried print was a good halftone image of high definition.

Due to the relatively high price of this water-miscible solvent, i.e.the n-vinyl pyrrolidone, comparted to the other materials used in theformulation, the final material cost was considered uneconomic. Tooffset this, a calcium carbonate extender was introduced into thecomposition to obtain a third embodiment with an acceptable raw materialcost. A mixture of photoinitiators was also used in place of the singletype. A specific formulation of this third embodiment, which likewisehad the resin amounting to 50% of the emulsion, is given in Example 3.

    ______________________________________                                        Example 3              Parts by weight                                        ______________________________________                                        Emulsion Laromer* PE 55W.sup.(1)                                                                     63.3                                                   Aquadisperse Phthalo Blue GB EP.sup.(3)                                                              2.7                                                    N Vinyl Pyrrolidone.sup.(4)                                                                          5.0                                                    Omyalite* 95T Extender.sup.(5)                                                                       20.0                                                   Photoinitiator Irgacure* 651.sup.(6)                                                                 6.0                                                    Photoinitiator Quantacure* ITX.sup.(7)                                                               3.0                                                    ______________________________________                                    

A composition formulated as in Example 3 was printed and dried in thesame manner as for Example 1. The resultant dried print was a good halftone image of high definition.

Samples of four colors Trichromatic yellow, magenta, cyan and black weremade for container storage stability trials.

After four weeks storage, the magenta and black inks had gelled whereasthe yellow and cyan were unchanged. Further work was carried out toimprove storage stability. In order to retain screen stability and aneconomic raw material cost, a fourth embodiment was devised in which then-vinyl pyrrolidone and the photoinitiator mixture were replaced by asolvent, ethoxy-propanol, and a single initiator compound rather thanthe mixture of photoinitiators. The calcium carbonate extender was alsoomitted as this was not now required to obtain an acceptable rawmaterial cost. A thickening agent was introduced to maintain the ink ata printable viscosity. Slight improvements in screen stability wereobtained with this embodiment by the introduction of small amounts of ahumectant/surfactant compound and of a silicone emulsion lubricant. Aspecific formulation of this fourth embodiment, in which (as before) theresin amounted to 50% of the emulsion, is provided in Example 4.

    ______________________________________                                        Example 4              Parts by weight                                        ______________________________________                                        Laromer* PE 55W.sup.(1)                                                                              75.2                                                   Darocur* 1173.sup.(2)  2.9                                                    Ethoxy Propanol.sup.(8)                                                                              9.7                                                    Curlout Plus*.sup.(9)  5.8                                                    Alcoprint* PTF.sup.(10)                                                                              0.5                                                    Alcoprint* PHL.sup.(11)                                                                              1.0                                                    Alcoprint PSJ.sup.(12) 1.9                                                    Aquadisperse Phthalo Blue GB EP.sup.(3)                                                              3.0                                                    ______________________________________                                    

A composition formulated as in Example 4 was printed and dried in thesame manner as for Example 1 The resultant dried print was a good halftone image of high definition.

The storage stability of trichromatic yellow, magenta, cyan and blackprinting inks with this latest formulation were then retested and foundto be satisfactory.

To provide a completely aqueous-based composition avoiding the use ofany inflammable solvents, a fifth embodiment was devised in which theethoxy propanol was replaced by a mixture of water and an acrylicmonomer -- Tripropylene glycol diacrylate (T.P.G.D A.) -- formaintaining the appropriate dispersion of the resin solids. A specificformulation of this fifth embodiment is provided in Example 5.

    ______________________________________                                        Example 5              Parts by weight                                        ______________________________________                                        Laromer* PE 55W.sup.(1)                                                                              61.6                                                   Darocur* 1173.sup.(2)  3.1                                                    Acrylic Monomer T.P.G.D.A..sup.(13)                                                                  7.7                                                    Water                  15.4                                                   Curlout Plus*.sup.(9)  5.7                                                    Alcoprint* PTF.sup.(10)                                                                              0.5                                                    Alcoprint* PHL.sup.(11)                                                                              1.0                                                    Alcoprint* PSJ.sup.(12)                                                                              2.0                                                    Aquadisperse* Phthalo Blue GB EP.sup.(3)                                                             3.0                                                    ______________________________________                                    

A composition formulated as in Example 5 was printed and dried in thesame manner as for Example 1 . The resultant dried print was a good halftone image of high definition

All the above-mentioned tests were carried out using 60"×40" (1.5mm×1m)machine glazed (M.G.) Poster Paper. It was found that when heavydeposits of color were used across the whole area of the paper, a highdegree of curl at the edges of the paper was experienced if the firstcolor printed down onto the paper was not a non-aqueous UV-curing ink(e.g. such as that of Example 6 below), or was not an organicsolvent-based printing ink (e.g such as that of Example 7 below), or wasnot an ink of a high solids/low water composition (e.g. such as that ofExample 8 below), i.e. an ink which contains less than 20% water.

    ______________________________________                                        Example 6 (referred to above)                                                                      Parts by weight                                          ______________________________________                                        Isol* Phthalo Blue GB PE 370.sup.(14)                                                              1.5                                                      Synocure* 3101.sup.(15)                                                                            50.0                                                     Acrylic Monomer T.P.G.D.A..sup.(13)                                                                33.4                                                     Quantacure* ITX.sup.(7)                                                                            2.9                                                      N. Methyl Diethanolamine.sup.(17)                                                                  1.9                                                      Irgacure 651.sup.(6) 5.7                                                      20cs Dimethyl Silicone Fluid.sup.(16)                                                              1.0                                                      Thickening Agent Cab-O-Sil* M5.sup.(18)                                                            1.7                                                      Matting Agent TS100.sup.(19)                                                                       1.9                                                      ______________________________________                                    

A composition formulated as in Example 6 was printed and dried in thesame manner as for Example 1. The resultant dried print was a good halftone image of high definition.

    ______________________________________                                        Example 7 (referred to above)                                                                      Parts by weight                                          ______________________________________                                        Piccolastic* A5.sup.(20)                                                                           1.67                                                     Ethoxy Propanol.sup.(8)                                                                            9.33                                                     N Propanol.sup.(21)  4.33                                                     Di-octyl Phthalate.sup.(22)                                                                        1.67                                                     Arcosolve* PM Acetate.sup.(23)                                                                     26.00                                                    Predisol* Phthalo Blue GBPC.sup.(24)                                                               1.56                                                     Dispercel* Thixotrope 27E.sup.(25)                                                                 7.00                                                     Xylene.sup.(26)      10.67                                                    Shellsol* A.sup.(27) 16.00                                                    Ethocel* 7 CPS.sup.(28)                                                                            15.33                                                    GB Ester.sup.(29)    6.44                                                     ______________________________________                                    

A composition formulated as in Example 7 was printed through a screenmade from 140 threads per cm polyester mesh. The stencil was made fromdirect emulsion using a half tone positive. The print was produced on aSvecia cylinder action screen printing press. The ink was dried througha warm air jet dryer. The resultant dried print was a good half toneimage of high definition.

    ______________________________________                                        Example 8 (referred to above)                                                                       Parts by Weight                                         ______________________________________                                        Darocur* 1173.sup.(2) 3.0                                                     Water                 15.0                                                    Aquadisperse Phthalo Blue GB EP.sup.(3)                                                             3.0                                                     UV Oligomer 85-578/79.sup.(30)                                                                      77.5                                                    Alcoprint* PTF.sup.(10)                                                                             0.5                                                     Silicone Antifoam S.882.sup.(31)                                                                    1.0                                                     ______________________________________                                    

A composition formulated as in Example 8 was printed and dried in thesame manner as for Example 1. The resultant dried print was a good halftone image of high definition.

It was unexpectedly found that once the first (cyan) ink had beenprinted in a non-aqueous UV-curing printing ink (e.g. of Example 6), orin an organic solvent-based printing ink (e.g. of Example 7), or in ahigh solid, low screen ink (e.g. of Example 8) having 20% or less water,then water based inks according to Examples 1 to 5 -- which contain atleast 40, water -- could nevertheless be used as additional colorswithout producing unacceptable curl of the paper, i.e. withoutpreventing feeding of the printed sheet again through the screenprinting machine.

The water-based inks of Examples 1 to 5, when cured only by UV radiationwere found to have a wet rub-resistance not adequate for all purposes,and to have a variable gloss level. Experiments were carried out withinfra red heating just before UV curing of the water-based inks waseffected. This technique produced prints with good wet rub-resistanceand with a substantially uniform level of gloss. It is thought that thiswas due to the removal of excess water by the infrared heating. It wasalso found that more efficient water removal could be achieved by usinga jet air dryer to force cold air over the print. It is considered thatexcess water might be removed, additionally or alternatively, bymicrowave or radio frequency drying.

Tests were conducted in pasting up the individual sheets to producehoarding posters, and starch based pastes (obtained from WilsonsAdhesives and Morris Greenhaugh) were used for these tests. The surfaceof the final prints produced in accord with the above Examples was foundto accept the starch pastes used by bill-posters more readily thanprints printed with the conventional screen inks which are currently ingeneral use. Prints produced with the water-based inks of Examples 1 to5, when dried only by UV radiation, showed excellent adhesion propertieswith the starch adhesives. Such prints, when dried both by infra-red andby UV radiation, showed a reduction in adhesion properties but this wasstill an improvement on that attainable with multi-color prints producedwith the standard organic solvent based screen printing inks.Nevertheless, by subjecting the final prints that had been dried by bothinfrared and UV radiation to corona discharge, this reduction inadhesion properties was overcome and prints with good gloss and wet-rubresistance were still obtained. In a preferred example, prints dried byinfra-red and UV radiation were treated to 73 dynes/cm using a ShermanTreaters Corona Discharge Machine. These prints showed the sameexcellent adhesion properties that were obtained by just drying with UVradiation.

Notes * means Trade Mark

1. Laromer * PE 55W is a 50% emulsion of a polyester acrylate in waterobtainable from B.A.S.F.

2. Darocur* 1173 is a Hydroxy-2-methyl-1-propan-1-one obtainable from E.Merck

3. Aquadisperse* Phthalo Blue GB EP is an aqueous dispersion of pigmentBlue 15 obtainable from Tennant-K.V.K.

4. n-vinyl pyrrolidone is a UV reactive solvent obtainable from B.A.S.F.

5. Omyalite* 95T is a calcium carbonate extender obtainable from Croxton& Garry.

6. Irgacure* 651 is benzil dimethyl ketal obtainable from Ciba Geigy.

7. Quantacure* ITX is isopropylthioxanthone obtainable from WardBlenkinsop.

8. ethoxy propylene glycol ether obtainable from B.P. Chemicals.

9. Curlout* Plus is a modified acrylic solution polymer obtainable fromAmerican Carbonyl Inc.

10. Alcoprint* PTF is an acrylic copolymer in mineral oil thickerobtainable from Allied Colloids.

11. Alcoprint* PHL is a humectant and surfactant blend obtainable fromAllied Colloids.

12. Alcoprint* PSJ is a silicone emulsion softner/lubricant obtainablefrom Allied Colloids.

13. T.P.G.D.A. is a tripropylene glycol diacrylate obtainable fromDegussa.

14. Isol* Phthalo Blue GBP 370 is Pigment Blue 15 obtainable fromTennant K.V.K. Ltd.

15. Synocure* 3101 is an epoxy acrylate obtainable from Cray ValleyProducts Limited.

16. Dimethyl silicone fluid 20csV viscosity obtainable from BasildonChemical Company Limited.

17. N-Methyl diethanolamine is a tertiary amine, obtainable fromB.A.S.F.

18. Cab-O-Sil* M5 is fumed silica obtainable from Cabot Carbon.

19. TS100 is a silica matting agent obtainable from Degussa.

20. Piccolastic* is a liquid styrene resin obtainable from Hercules Ltd.

21. N.Propanol is obtainable from B.P. Chemicals.

22. Di-octyl phthalate is obtainable form Charles Tennant (London) Ltd.

23. Arcosolve* PM Acetate is propylene glycol monomethyl ether acetateobtainable from Hays Chemical UNALCO.

24. Predisol* Phthalo Blue GBPC is a nitrocellulose dispersion ofpigment Blue 15 obtainable from Tennant KVK.

25. Dispercel* Thixotrope 27E is a nitrocellulose dispersion of Bentone27E gellant.

26. Xylene is obtainable from Shell Chemicals

27. Shellsol* A is an isomeric mixture of trimethyl benzenes obtainablefrom Shell Chemicals.

28. Ethocel* 7 CPS is ethyl cellulose resin otainable from DowChemicals.

29. GB Ester is butyl glycolate obtainable from Wacker Chemicals.

30. UV Oligomer 85-578/79 is a UV resin with 5% water content availablefrom Hans Rahn & Co, Zurich.

31. Silicone Antifoam S.882 is a water miscible antifoam available fromWacker Chemicals.

We claim:
 1. A method for minimizing substrate edge-curl in a processwhen a substrate is screen printed with a water-based screen printingink comprising the steps of:(a) carrying out a first screen printingusing an ink which produces a minimal curl in the substrate edge; andthen (b) carrying out at least one subsequent screen printing on theprinted substrate from step (a) using a water-based ink --,whereby anyresulting curl is less than that which would be obtained if the firstscreen printing were with said water-based ink--.
 2. A method accordingto claim 1, wherein said first silk screen printing is in a first colorand each said subsequent printing is in different color.
 3. A methodaccording to claim 1, wherein the printing ink for said first screenprinting comprises a non-aqueous printing ink that is at least partiallycurable by irradiation.
 4. A method according to claim 3, wherein saidnonaqueous printing ink that is curable by irradiation comprises one ormore photoinitiators and is curable by irradiation comprisingelectromagnetic radiations in the ultraviolet light waveband.
 5. Amethod according to claim 3, wherein said nonaqueous printing ink iscurable by irradiation with an electron beam.
 6. The method of claim 3wherein the non-aqueous ink comprises:

    ______________________________________                                                          Parts by Weight                                             ______________________________________                                        Pigment Blue 15     1.5                                                       Epoxy acrylate      50.0                                                      Tripropylene glycol diacrylate                                                                    33.4                                                      Isopropylthioxanthone                                                                             2.9                                                       N-methyl diethanolamine                                                                           1.9                                                       Benzil dimethyl ketal                                                                             5.7                                                       Dimethyl silicone fluid                                                                           1.0                                                       Fumed silica        1.7                                                       Silica matting agent                                                                              1.9.                                                      ______________________________________                                    


7. A method according to claim 1, wherein the printing ink for saidfirst screen printing comprises an organic solvent based printing ink.8. The method of claim 7 wherein organic solvent based printing inkcomprises:

    ______________________________________                                                             Parts by Weight                                          ______________________________________                                        Liquid styrene resin   1.67                                                   Ethoxy propylene glycol ether                                                                        9.33                                                   N-propanol             4.33                                                   Di-octyl phthalate     1.67                                                   Propylene glycol monomethyl                                                                          26.00                                                  ether acetate                                                                 Nitrocellulose dispersion of                                                                         1.56                                                   pigment Blue 15                                                               Nitrocellulose dispersion of                                                                         7.00                                                   Bentone 27E gellant                                                           Xylene                 10.67                                                  Isomeric mixture of trimethyl benzenes                                                               16.00                                                  Ethyl cellulose resin  15.33                                                  Butyl glycolate        6.44.                                                  ______________________________________                                    


9. A method according to claim 1, wherein the printing ink for saidfirst screen printing comprises an aqueous ink of low water and highsolids content.
 10. The method of claim 9 wherein the said aqueous inkcomprises:

    ______________________________________                                                             Parts by Weight                                          ______________________________________                                        Hydroxy-2-methyl-1-propan-1-one                                                                      3.0                                                    Water                  15.0                                                   Aqueous dispersion of pigment Blue 15                                                                3.0                                                    UV resin with 5% water content                                                                       77.5                                                   Acrylic copolymer in mineral oil                                                                     0.5                                                    thickener                                                                     Water-miscible antifoam                                                                              1.0.                                                   ______________________________________                                    


11. A method according to claim 1, wherein said water-based ink for eachsaid subsequent screen printing comprises at least 40% water.
 12. Amethod according to claim 1, wherein the water-based printing ink foreach said subsequent screen printing is at least partially curable byirradiation.
 13. A method according to claim 12, wherein saidwater-based printing ink that is at least partially curable byirradiation has a composition comprising one or more photoinitiators andis curable by irradiation comprising electromagnetic radiations in theultraviolet light waveband.
 14. A method according to claim 12, whereinsaid water-based ink is curable by irradiation with an electron beam.15. A method according to claim 1, including subjecting the water-basedprinting ink for each said subsequent screen printing to heat or tothermal radiation, and then curing.
 16. A method according to claim 1,including subjecting the water-based printing ink for each saidsubsequent screen printing to electromagnetic radiations in the infraredlight waveband, and then curing.
 17. A method according to claim 1,wherein the water-based printing ink for each said subsequent screenprinting comprises an unsaturated acrylate resin.
 18. A method accordingto claim 1, wherein the water-based printing ink for each saidsubsequent screen printing comprises a polyester acrylate resin.
 19. Amethod according to claim 1, wherein the water-based printing ink foreach said subsequent screen printing comprises an emulsion of a resin inwater.
 20. A method according to claim 19, wherein the emulsion has thesaid resin wholly, or at least substantially, in dispersed phase andwholly, or at least substantially, insoluble in water, the water beingthe continuous phase of the emulsion.
 21. A method according to claim19, wherein the resin comprises between 30% to 60% of the emulsion. 22.A method according to claim 19, wherein the resin comprises 50% of theemulsion.
 23. A method according to claim 1, to screen print a pluralityof colors upon a substrate , including subjecting, after printing, theprinted substrate to corona discharge to render the substrate suitablefor mounting by use of a starch-based adhesive.
 24. The method of claim1 wherein the ink in step (a) is selected from the group consisting ofradiation curable non-aqueous printing inks, organic solvent based inks,and water-based inks having a water content sufficiently low to minimizeedge-curling of the substrate.
 25. A method according to claim 1 whereinthe waterbased printing ink comprises:

    ______________________________________                                                             Parts by Weight                                          ______________________________________                                        50% emulsion of a polyester                                                                          95.3                                                   acrylate in water                                                             Hydroxy-2-methyl-1-propan-1-one                                                                      2.0                                                    Aqueous dispersion of pigment Blue 15                                                                2.7.                                                   ______________________________________                                    


26. A method according to claim 1 wherein the waterbased printing inkcomprises

    ______________________________________                                                             Parts by Weight                                          ______________________________________                                        50% emulsion of a polyester                                                                          85.3                                                   acrylate in water                                                             Hydroxy-2-methyl-1-propan-1-one                                                                      2.0                                                    Aqueous dispersion of pigment Blue 15                                                                2.7                                                    N-vinyl pyrrolidone    10.0.                                                  ______________________________________                                    


27. A method according to claim 1 wherein the waterbased printing inkcomprises:

    ______________________________________                                                             Parts by Weight                                          ______________________________________                                        50% emulsion of a polyester                                                                          63.3                                                   acrylate in water                                                             Aqueous dispersion of pigment Blue 15                                                                2.7                                                    N-vinyl pyrrolidone    5.0                                                    Calcium carbonate extender                                                                           20.0                                                   Benzil dimethyl ketal  6.0                                                    Isopropylthioxanthone  3.0.                                                   ______________________________________                                    


28. A method according to claim 1 wherein the waterbased printing inkcomprises:

    ______________________________________                                                             Parts by Weight                                          ______________________________________                                        50% emulsion of a polyester                                                                          75.2                                                   acrylate in water                                                             Hydroxy-2-methyl-1-propan-1-one                                                                      2.9                                                    Ethoxy propylene glycol ether                                                                        9.7                                                    Modified acrylic solution polymer                                                                    5.8                                                    Acrylic copolymer in mineral oil                                                                     0.5                                                    thickener                                                                     Humectant and surfactant blend                                                                       1.0                                                    Silicone emulsion softener/lubricant                                                                 1.9                                                    Aqueous dispersion of pigment Blue 15                                                                3.0.                                                   ______________________________________                                    


29. The method according to claim 1 wherein the waterbased printing inkcomprises:

    ______________________________________                                                             Parts by Weight                                          ______________________________________                                        50% emulsion of a polyester                                                                          61.6                                                   acrylate in water                                                             Hydroxy-2-methyl-1-propan-1-one                                                                      3.1                                                    Tripropylene glycol diacrylate                                                                       7.7                                                    Water                  15.4                                                   Modified acrylic solution polymer                                                                    5.7                                                    Acrylic copolymer in mineral oil                                                                     0.5                                                    thickener                                                                     Humectant and surfactant blend                                                                       1.0                                                    Silicone emulsion softener/lubricant                                                                 2.0                                                    Aqueous dispersion of pigment Blue 15                                                                3.0.                                                   ______________________________________                                    